Several human conditions are characterized by distinctive lipid compositions of tissues, cells, membranes, and extracellular regions or structures. For example, in atherosclerosis, cholesterol (unesterified, esterified, and oxidized forms) and other lipids accumulate in cells and in extracellular areas of the arterial wall and elsewhere. These lipids have potentially harmful biologic effects, for example, by changing cellular functions, including gene expression, and by narrowing the vessel lumen, obstructing the flow of blood. Removal of these lipids would provide numerous substantial benefits. Moreover, cells, membranes, tissues, and extracellular structures will benefit in general from compositional alterations that include increasing resistance to oxidation and oxidative damage, such as by increasing the content and types of anti-oxidants, removing oxidized material, and increasing the content of material that is resistant to oxidation. In aging, cells have been shown to accumulate sphingomyelin and cholesterol, which alter cellular functions. These functions can be restored in vitro by removal of these lipids and replacement with phospholipid from liposomes. A major obstacle to performing similar lipid alterations in vivo has been disposition of the lipids mobilized from tissues, cells, extracellular areas, and membranes. Natural (e.g., high-density lipoproteins) and synthetic (e.g., small liposomes) particles that could mobilize peripheral tissue lipids have a substantial disadvantage: they deliver their lipids to the liver in a manner that disturbs hepatic cholesterol homeostasis, resulting in elevations in plasma concentrations of harmful lipoproteins, such as low-density lipoprotein (LDL), a major atherogenic lipoprotein. There exist a need for better methods to manipulate the lipid content and composition of peripheral tissues, cells, membranes, and extracellular regions in vivo.
The intravenous administration of cholesterol-poor phospholipid vesicles (liposomes) or other particles that transport cholesterol and other exchangeable material from lipoproteins and peripheral tissues, including atherosclerotic arterial lesions, to the liver produces substantial derangements of hepatic cholesterol homeostasis, such as enhanced hepatic secretion of apolipoprotein-B, and suppression of hepatic LDL receptors. The hepatic derangements lead to increase plasma concentrations of LDL and other atherogenic lipoproteins. Increased concentrations of LDL or other atherogenic lipoproteins will accelerate, not retard, the development of vascular complications. Deranged hepatic cholesterol homeostasis can also be manifested by abnormal regulation of genes, such as a gene for the LDL receptor, a gene for HMG--CoA reductase, a gene for cholesterol 7-alpha hydroxylase, and a gene regulating a function involved in cholesterol homeostasis. There exists a need for methods or compounds that can produce a removal of cholesterol and other exchangeable material, from peripheral cells, tissues, organs, and extracellular regions, and that can produce a delivery of material, such as phospholipids, to cells, tissues, or organs, extracellular regions, but without harmfully disrupting hepatic cholesterol homeostasis and plasma concentrations of atherogenic lipoproteins.
The invention described herein provides methods and compositions related to the removal of cholesterol and other exchangeable material from peripheral tissues, and otherwise altering peripheral tissue composition, while controlling plasma concentrations of LDL and other atherogenic lipoproteins and avoiding harmful disruptions of hepatic cholesterol homeostasis.